Conventionally, there is a vehicle door lock device that transmits a rotational operation of a key cylinder to a lock/unlock mechanism with a coupling member. As an example of the vehicle door lock device, Patent Literature 1 discloses a technique of a vehicle-door opening/closing device that includes a turning-force transmission unit having a driven-side turning member that is detachably coupled to a key-operation-force input member to be incapable of relatively turning, a driving-side turning member that is detachably coupled to the other end part of a turning rod to be incapable of relatively turning, and a transmission member that transmits a turning force from the driving-side turning member to the driven-side turning member, which members are housed in an extension case. In the vehicle-door opening/closing device described in Patent Literature 1, the extension case is detachably attached to a casing of a door lock device so as to protrude from the casing.